* {
    margin: 0;
    padding: 0;
    font-family: 'Heiti SC';
}

body {
    padding: 20px;
}

.nav-link {
    position: relative;
    padding: .55em 1.1em;
    color: #fff;
    font-size: 18px; /* 字体大小照写即可 */
    background-color: #666666;
    text-decoration: none;
    display: inline-block;
}

.nav-link::after {
    content: '';
    position: absolute;
    left: 0;
    top: 100%;
    width: 100%;
    border-top: 10px solid #666; /* 底部三角多高就改多少px */
    border-left: 2.6em solid transparent;
    border-right: 2.6em solid transparent;
    box-sizing: border-box;
}
